Abstract
An infective prey has the potential to infect, kill and consume its predator. Such a prey-predator relationship fundamentally differs from the predator-prey interaction because the prey can directly profit from the predator as a growth resource. Here we present a population dynamics model of partial role reversal in the predator-prey interaction of two species, the bottom dwelling marine deposit feeder sea cucumber Apostichopus japonicus and an important food source for the sea cucumber but potentially infective bacterium Vibrio splendidus. We analyse the effects of different parameters, e.g. infectivity and grazing rate, on the population sizes. We show that relative population sizes of the sea cucumber and V. Splendidus may switch with increasing infectivity. We also show that in the partial role reversal interaction the infective prey may benefit from the presence of the predator such that the population size may exceed the value of the carrying capacity of the prey in the absence of the predator. We also analysed the conditions for species extinction. The extinction of the prey, V. splendidus, may occur when its growth rate is low, or in the absence of infectivity. The extinction of the predator, A. japonicus, may follow if either the infectivity of the prey is high or a moderately infective prey is abundant. We conclude that partial role reversal is an undervalued subject in predator-prey studies.
Highlights
The ability of a prey to utilize the predator as a food source is referred to as a role reversal in predator-prey interaction [1,2,3]
Because bacteria form an important food source for the sea cucumber, A. japonicus can be treated as a predator to V. splendidus
We address the problem of partial role reversal in the predator-prey interaction by presenting a predator-infective prey model to analyse the dynamics and coexistence of the species
Summary
The ability of a prey to utilize the predator as a food source is referred to as a role reversal in predator-prey interaction [1,2,3]. Because bacteria form an important food source for the sea cucumber, A. japonicus can be treated as a predator to V. splendidus. The extinction depends on the infectivity of the prey, its population size as well as the grazing rate of the predator. Let C, S and I denote the abundances of the prey, susceptible predator and infected predator populations, respectively. The generalist predator population (S) grows by grazing the sediment, which hosts the Vibrio prey (C) (Fig 1) Both species use other resources for growth,. A significant aspect in our predator-prey interaction is that both the prey and the predator are only a part of a food web Both species have a base growth rate that is independent of their mutual interaction, and they both are able to grow independently according to the respective carrying capacity of the environment. Inserting I into Eqs (1) and (2) and dividing the resulting equations by C and S, respectively, we get
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